Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 25th, 2021 - 7:00AM
Expires
Fri, March 26th, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE at all elevations but could rise to CONSIDERABLE depending on how much snow falls throughout the day. If this storm produces, triggering storm slabs will be likely. This storm is forecast to favor Girdwood. In addition, it is still possible to trigger an avalanche on weak layers of snow buried 1-3’ deep. The most likely places to trigger this type of avalanche will be on steep slopes with old hard wind affected snow. New snow could make it more challenging to identify where these stiff slabs are lingering. Assess the snowpack as you travel, identify areas of concern and evaluate terrain consequences.

Special Announcements

Heading to Hatcher Pass? Be sure to check the Thursday Conditions Summary at hpavalanche.org.

Thanks to our sponsors!
Thu, March 25th, 2021
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Snow started falling this morning and will continue to fall for most of the day today (fingers crossed we avoid the “R” word). This weather pattern is already favoring Girdwood over Turnagain. Five inches have already fallen in Girdwood with only an inch registering on the Center Ridge SNOTEL.  An additional 4-7″ is forecast to fall today. The avalanche danger will be really dependent on how much snow we get and how well it bonds to existing snow surfaces.  The winds aren’t supposed to be strong but if they kick up a bit they could add to the slab building in the Alpine. Paying attention to changing conditions will be crucial today. If this storm really produces, watch for storm slabs to form. Southerly slopes have a sun crust, northerly protected slopes have loose faceted snow and wind affected terrain has a hard wind crust. New snow is not expected to bond well to any of these surfaces.  The temperatures will also rise, potentially creating a bit of an ‘upside down’ storm situation with heavier snow falling on lighter snow. The other factor to consider is that triggering a storm slab avalanche could overload our layers of lurking buried weak snow and produce a larger avalanche (more in Problem 2).

The rain/snowline may rise to around 500′. Rain on snow may produce small roller balls and mini wet loose avalanches.

Dry loose snow avalanches: Steep slopes that have been sheltered from the wind have up to a foot of loose snow sitting on top of firm surfaces. New snow will add volume to this set-up. It will be easy to trigger dry loose avalanches (sluffs), and they could pickup enough speed to carry a person. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

Snow surface buffet – sun crust, soft facets and hard wind affected snow. 3.24. 21

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Today’s storm will cover up the existing snow surfaces, making it a bit more challenging to figure out where the old wind affected snow is. It could will also add more load and  potentially create more of a slab. Our concern continues to be finding a spot where there is a slab over the layers of buried weak snow in the upper 1-3′ of the snowpack.  This is where we think it is still possible to trigger a persistent slab avalanche. The most recent human triggered avalanches were on steep slopes with hard wind affected snow sitting on top of facets and/or surface hoar. These buried layers of weak snow seem to be widespread across the forecast area. The part that remains variable is the character of the snow resting on top of the weak snow. Figuring out whether or not there is a slab is key to safe travel in steep terrain. Be on the lookout for indications of previous wind-loading under the new snow, including stiff snow on or a hollow, ‘punchy’ feeling slab. The most suspect terrain will likely be at upper elevations, especially immediately below ridgelines, in cross-loaded gullies, and below convexities. As always, watch for signs of instability, use good travel protocol, and think about terrain consequences. This type of avalanche issue might allow you to get well out on to the slope before the avalanche releases and it might not be the first person that triggers the avalanche.

Buried surface hoar sitting under hard wind affected snow just off the ridgeline on the north side of Tincan. 3.24.21.

Another layer of buried surface hoar 2′ down in a snow pit on the north side of Tincan, 3.24.21. The results of a Propagation Saw Test indicated that there is still a possibility of triggering an avalanche on this layer.

 

.

Weather
Thu, March 25th, 2021
Yesterday: Skies were partly cloudy becoming overcast in the afternoon. Winds were mostly light and variable. Temperatures were in the 20°Fs to mid 30°Fs. A few valley weather stations saw highs into 40°Fs. Overnight skies were cloudy with light snow beginning around 2 am. Winds remained light and variable with temperatures in the 20°Fs. Today: Skies will be cloudy with snow likely throughout the day, with up to a foot of snow expected.  Rain/snow line is forecast to rise to 500'. Winds will be easterly 5-15 mph with gusts into the 20s. Temperatures will be in the 20°Fs at upper elevations and 30°Fs near sea level. Clouds will decrease overnight and winds will shift to the west. Temperatures will be in the mid teens to mid 20°Fs. Tomorrow: Mostly sunny skies with temperatures in the mid 20°Fs to mid 30°Fs. Winds will be northwesterly 5-15 mph. Clouds move in again overnight and linger through Saturday with some partly sunny skies in the forecast for Sunday. There is talk of a more active pattern next week but we shall see if that pans out. PRECIPITATION 24-hour data (6am - 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 24 1 0.1 111
Summit Lake (1400') 26 1 0.1 46
Alyeska Mid (1700') 26 5 0.2 114
RIDGETOP 24-hour data (6am - 6am)
Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17 W 8 31
Seattle Ridge (2400') 21 var 4 12
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/18/21 Turnagain Observation: Tincan Ridge
04/30/21 Turnagain Observation: Sunburst
04/27/21 Turnagain Observation: Tincan Ridge
04/26/21 Turnagain Observation: Magnum
04/25/21 Turnagain Observation: Sunburst
04/24/21 Turnagain Observation: Airplane obs
04/24/21 Turnagain Observation: Corn biscuit
04/23/21 Turnagain Avalanche: Lynx Ck Drainage
04/23/21 Turnagain Avalanche: Sunburst
04/23/21 Turnagain Observation: Center Ridge Turnagain pass
Riding Areas
Updated Tue, June 01st, 2021

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

Subscribe to Turnagain Pass
Avalanche Forecast by Email

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.